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Role of bacteria in the North Sea ecosystem

par Billen, Gilles ;Joiris, Claude ;Meyer-Reil, Lutz;Linderboom, Han
Référence Netherlands journal of sea research, 26, 2-4, page (265-293)
Publication Publié, 1990-11

Article révisé par les pairs

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Résumé :

Since about 15 years methods available to assess the role of bacteria in organic matter cycling of aquatic ecosystems have been considerably improved. Their application to the North Sea deeply modified the vision of the ecological structure of this ecosystem which prevailed in the early seventies, as summarized e.g. by STEELE (1974). A critical examination of the methodology utilized for measuring standing stock and activities of bacteria in the water column and the sediments of the North Sea is presented and the results of these measurements summarized. Measurements of planktonic bacterial biomass show important seasonal and geographical variations, related, with a delay of about 10 days, to phytoplanktonic development. Assessment of the standing stock and turnover rate of high molecular weight dissolved organic matter and monomeric substrates provides data consistent with the view that extracellular enzymatic hydrolysis of polymers is limiting the rate of organic matter utilization, while uptake of direct substrates is rapid and maintains their concentration at a near constant level. The flux of organic matter flowing through the planktonic bacterial compartment is evaluated to about 110gC/m2.yr in the coastal continental zone, i.e. 57% of net primary production. Bacterial production rates show a growth yield in the range 0.1 to 0.4. In the Central North Sea data are lacking to allow accurate estimation of planktonic bacterial activity on annual basis. The available information suggests that a lower percentage of primary production is used by bacteria there. Data concerning bacterial biomass and activity in the benthos are even less numerous than for the planktonic phase. A crude estimate of the flux of organic matter sedimentation based on sediment traps measurements on the one hand, and of organic matter utilization rates by benthic organisms (including both bacteria and meiofauna) derived from oxidant or nutrient budgets on the other hand, yield values in the range 50-100 gC/m2yr in the continental coastal zone and about 10-40 gC/m2yr in the Central North Sea. The authors stress the paucity of data concerning bacterial activity in the benthic phase and in the Central and northern North Sea. © 1990.